toolchain/wrapper.sh: fix remaining shellcheck warnings

toolchain/wrapper.sh: fix remaining shellcheck warnings

Fixes following warnings:

 In target/toolchain/files/wrapper.sh line 18:
 REALNAME=$(readlink -f $0)
                        ^-- SC2086: Double quote to prevent globbing and word splitting.
 --
 In target/toolchain/files/wrapper.sh line 20:
 REALNAME_BASE=$(basename $REALNAME)
                          ^-------^ SC2086: Double quote to prevent globbing and word splitting.
 --
 In target/toolchain/files/wrapper.sh line 21:
 REALNAME_DIR=$(dirname $REALNAME)
                        ^-------^ SC2086: Double quote to prevent globbing and word splitting.
 --
 In target/toolchain/files/wrapper.sh line 74:
 		exec $TARGET_TOOLCHAIN_TRIPLET-$BINARY.bin $GCC_SYSROOT_FLAGS $TARGET_FUNDAMENTAL_CFLAGS $TARGET_ROOTFS_CFLAGS "$@"
                     ^-----------------------^ SC2086: Double quote to prevent globbing and word splitting.
 --
 In target/toolchain/files/wrapper.sh line 77:
 		exec $TARGET_TOOLCHAIN_TRIPLET-$BINARY.bin $LD_SYSROOT_FLAGS $TARGET_FUNDAMENTAL_LDFLAGS "$@"
                      ^-----------------------^ SC2086: Double quote to prevent globbing and word splitting.
 --
 In target/toolchain/files/wrapper.sh line 80:
 		exec $TARGET_TOOLCHAIN_TRIPLET-$BINARY.bin $TARGET_FUNDAMENTAL_ASFLAGS "$@"
                      ^-----------------------^ SC2086: Double quote to prevent globbing and word splitting.
 --
 In target/toolchain/files/wrapper.sh line 83:
 		exec $TARGET_TOOLCHAIN_TRIPLET-$BINARY.bin "$@"
                      ^-----------------------^ SC2086: Double quote to prevent globbing and word splitting.

Signed-off-by: Petr Štetiar <ynezz@true.cz>